Telephone-exchange system.



T,.G. MAHHN. TELEPHONE- EXCHANGE SYSEM. vAPPLICATIONmin' MAY 5. i910.

@armed om.. 5,1915.

mm, KWMM 10S,

, 21 SHEETS-SHEET-Z.

TALBoT G. MARTIN, 0F CHICAGO, ILLINOIS, ASSIGNR TO AUTOMATIC ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

TELEPHONE-EXCHANGE SYSTEM.

Specification of Letters Patent.

Patente-d Oct. 5, MM5.

Application tiled May 6, 1910. Serial No. 559,815.

fo U whom it 'may concern.'

Be it known that I, TALBOT G. MARTIN, a citizen of the United States of America. and resident of Chicago, Cook county, Illinois, have. invented a certain new and useful Improvement in 'llelephone-Exchange Systems, of which the following is a specification.

My invention relates to telephone exchange 'systems of that kind in which automatic switches are employed at the exchange or central station for establishing connection between calling lines and called lines. A system of this kind may be either entirely automatic or it may be semi-automatic, depending upon circumstances, butin each case there are a suitable number of automatic switches for selecting trunks, or completing connections, or doing other parts of the work necessary to the establishment of a connec tion between calling and called lines.

My invention relates more particularly to a system of this kind in which the subscribers lines are provided with automatic switches, and in which one or more of said lines are provided with extensions, or with a pluralit)7 of substations, whereby several telephones are allotted to and common to one and the same line.

My invention contemplates 4an extension or party-line system of this general character in which the said extensions or partylines are provided with automatic trunkingy switches, ordinarily known as line switches, and in which two persons or subscribers on the same line may converse with each other without disturbing Athe normal condition of the automatic switch for such line` notwith-` standing that the current for talking puw poses is derived from a common 4battery or other source at the exchange or central sta tion, and regardless of the fact that talking current flows in the line immediately upon the taking down of any receiver thereon, no4,

operating grounds being necessary at th substations, in so far as the calling' of a subscriberls.- number is concerned,"the system being of the two-wire type for that purpose at least. .n

This invention is in the nature of an iinprovement ou the followin,- copending applicatioi'is'. Serial #522.065, liledoctober ll, 1h09; Serial #$422,462. (iledllllarch 2l, 1908; ScrialtfrOTl'O, iilcd July l2, 1.909; Serial #5346581, and' Mgmt i, 1910; sean #336,13l, filed January 3, 1910; Serial #o80,'-i01, led November 29.1969; Sei-igt #596310, sied December 10,1910; aaa serial #546,582, tiled March i, i910.

Ars will hereinafter more fully appear, it will be seen, however, that Vmy invention further contemplates a system of this kind in which a special ground is provided at each telephone on the extension or party` line, which ground is used merely for operating the non'numerical trunking switch of the said line, all otherswitches then being controlled, while the call is progressing, by using the two sides of the ii'ne in series. I

To the foregoing and other useful ends my invention consists in matters hereinafter set forth and claimed.

'In the 'accompanying drawings Figures 1 and 2v taken together represent diagram: matically a call from one partyline to another in a telephone exchange system enr bodying the principles of my invention. i

In Fig. 1 there is shownat A and A two automatic substationsallotted to the same line, which line terminates in the line lswitch (l. At D there is shown-a master switch which is used to keep the plungers of the line switches C opposite an idle trunk line. At E and F selector switches are shown.

At H (Fig. there is shown a connector switch, At L a ringing current generator is shown and at lsi a busy signaling,` machine is represented. .it C there is shown a line switclrsimilar to the line switch' C, The substations shown at tand A3 'are similar to those shown at A and These vsubstatons, like the substations- A and A', are allotted tothe same line which terminates in.

the line switch C. At B is represented a battery with its positive terminal preferably `grounded at G. 'Gf course, there may or rmay not be more than one battery B used with this system, depending upon the condi tions to be met, Also, as herein shown, only one set of ringers is shown bridged across each line. There may, however, be one or more sets used. ln orderto prevent tinkling of the ringer l2 by the impulses which operate the central oiirice switches, ordinary lOtl biased ringers may be used, biased in such direction Vas not to be aected by these op; eratmg impulses'. i"

oil

'6 and "i", impulse wheel 8 on which To provide means whereby the dill'erent other an independent buzzer circuit is em- .p .loyed, asrepresented at K (Fig. 1). This circuit consists essentiall7 ofthe ringers or hunters R and R', one for each substation. Current is supplied tothese buzzer-s by the battery Z1. All' herein shown. the substation consists ol he recei 2 switch hook 5L transmitter 4i pfislrbrtton 5. hook springs i are the impulse teeth il. impulse springs 10 and 11. ringer 12 and condenser 13. 'l`he iinpulse wheel S is secured to the shaft 1l, to which there is also secured a dial (not shown) containing finger holes.

The removal ol" the receiver 2 from its hook allows thehook to riseu which permits the engagement of the springs (i and 7. The engagement', of these springs closes a bridge across the conductors 15 and 16 through the. transmitter l, f receiver :2 and .fzprings 10 and 11. The conductors 1.5 and 1li terminate in the line switch (l at. the central ol'iice or exchange. The line sw :h (l is of the general type disclosed in Bri'ti l1 lat ent No. 26.301 ot' 1906. and in the liner/'croi Telephone Journal ol New York, N. Y., of June (L 1908. This switch is provided with the usual plunger arm 2l which is adapted to he attracted h v the magnet 1i. This ma `net comprises four windings, namely, the pullin winding 19, cut-oli winding Q0, line winding 21 an'd auxiliar)Y winding 22.l The magnetic circuit of the windings .21 and :22 is separate from that of the windings 19 and 20, so that the armature 23 and plunger arm 24 are affected only b v the windings 1f) and 20, and the windings "l1 and E22 allier-t oni)Y the armature 25. The winding 1 5)` when energized, operatively yattracts both the plunger arin 24 and armature 23, while the winding 20, when energized, will oni)7 pull np the armature 23, but will hold the plungen arm ,f-l, in an operated position after it has been pulled up byv the winding 19. The attraction' of the plunger arm thrusts a plunger (not shown) into a group of springs to loneedhe springs 26, 28, 230 and 32 into engagement with the springs Q7, 29, 31 and 33, i'cspectively, whereby the line conductors are extended to a lirst selector, such as the first selector l". Although only o ne group of springs (MP-33) is shown, there ma)7 he however` a plurality of such groups to which the plunger of the line switch (j hasaccess, each of which groups is the terminal ot a` trunk line leading to :i

first selector similar to the selector Efd The line conductor 1(5,is normally connected to ground at the switch C tlnongh the resist-- ance 18.

The plungers of the group ot' of which the switch C is a trolied'loy a common Ineeliain':A

line switches are coninipulse locking plate l0 are so lhere shown` llease magnet, rather called a master switch. This master switch controls the plungers` in auch a manner that the)v are normally held in a position oppo site an idle trunlt. The masterl switch Vl) comprises the rali-het wheel lll which is actuated hy thel armature It? ol the niotor magnet 53V and a hanh' o'l contacts fr which consists of a numhcr ol" individual segments 3T and a connnon segment ltl. The master switch also has the ci1'cuitcontrolling re lays 9H and Sli). The hanh ff is provided with a wiper il!) lol' keeping one olf the indiridual segments li in electrical conm-wflion with the common segment 2in'. lfilr means ol a snit` able mechanical connection tho rotary motion ot the ratchet wheel l-lis transmitted to the plunger shaft to gire said .shaft an oscil latory motion to more the plungers which are normalliy in register therewith hurl( and forth in liront olE the Lci'niinals ol' the Ntrunlts leading to the lirsl selectors. To [lal plunger shaft there is also secured a locking plate l() haring Ain its surface a nuinher olf openings. one of which is normali)Y engaged h v the pin l2 on the armature lil, The openings in the pin 4-2 can onliv engage au opening when the plungers thatare in. engagement with the plunger shalt lire directlyY opposite they ter minals ol a trunlt leading to a lirst selectin;

The selector switch shown at lil is of the general type disclosed in llnitcd States Let-- ters latent No. (Q1-3.321, granted March liu. 1906, to Keith` Erickson & ilrickson, hat, as

is modified to operate in' conjunction with a two-wire system that is.`

a system in which the 'central oll'ice mechanism is controlledover the two sides ol' the telephone line in series. Aimong other details, the selector E comprises the wipers il, l5 and l-(l mounted upon a shalt (not shown) which has a Vertical n'iotion con trolled hy the vertical magnet -l'i and a rntary .motion controlled hy the rotar-ii magnet #178. The calling suhscrihcr controls the operation of the switch through the inediiun ot the douhledxound line relay `lift 'l`he re leasel ot the selector is lirounht about h r means ot the release magnet 30. Battery curi-eht is supplied to the release magnet :is soon the shal'tis raised one or more steps thus lifting the arm 5]. and permitting the springs 52 and :i3 to engage. The selector released upon the energizatiou ol the rethan upon its deiinerfixation` as .shown in said selector partent` The relays ."i-l, 55 and titl are sims-acting relars-that is, their armatures are slow fallback after having once heen attracted. This slow action is usnallj,7 arcnmplislnal hv means o'lE a copper ring plaotd around thi, end ol' the core,` The selector also has a private magnet (il which controls the side switch comprising the wipers` lith 613 t'zl and 63.

positioned that the- .ber we will assume to be 2220. I

The selector l" is similar' to the selector lil.

The connector ll is of the type disclosed in l`nite'd States Letters latcnt No. 815.176. granted March lil. llllb. to Keith. Erickson et llriclson. and. like the selector. is modified to (uieratewith a two-wire system. Lilie the selector. the connector comprises a shaft upon which are the wipers (i3. lili and (3T. double-wound relay 13H; vertical ymagnet (19'. rotary magnet TU. Vrelease magnet T1 `and private magnet TL' which controls the side switch with its wipersl Til. il. T5. Tli and TT. 'the connector also has. in addition. the back-bridge relay 55 through which talking current issupplied to the called subscriber, and ringer. relay T which serres to disconnect the calling line trom and connect the ringing current generator L to the called line. (round is only supplied intermittently to the ringer relay through the interrupter TS. ri`he connector is also suppliedfwith a busy locking relay 5H. the function of which will be eti'ilained later.

.is lzet'ore stated. the line switch C and substations .i2 and A?" are similar to line switch t and substation A. respectively, or" Fig. 1.

llaring thus described the general character ot' the ailiparatus.which is used in the system embodying the principlesot' my invrention. l will now describe the process by 'which arcalling subscriber A. whose number we will assume to be 2221. establishes connection with the subscriber A. whose numill also descrioe how subscriber )t may conyerse with anj.r other station on his own line. substation for instance.

Ylien the subscriber A removes his receiver ilirepzliratory to making' the call. a

circuit s closed through line winding 2t ot the e lswitch C. rthis circuit extends from ground il through springs 75l and 80.

resistance 1S. line lconductor 1G. springs (i and which engage as soon as the switch hoch rises. impulse springs l1 and 10. receiver transmitter l. line conductor 15. springs S1, and S2 and line winding 21 to battery lead Sil. thence through battery B to ground (l. Since this circuit includes resistance 1F. .suliicient currentfdoes not low to cause winding 2l to attract the .armature 25. 'Therefore in order for subscriber to perate the line switch C. it is necessary fer him to press the button 5. which action completes a. new circuit through the line winding ill.. This circuit extends from ground t through conductor l5. springs Sl andFQ, line winding 2l to battery lead 82%. Sutiicient current now tiows through the winding 21 to attract the armature 25. which :arises the engagement of springs T9 and Si. A circuit is now completed through the pullin winding 1S) 'in series with winding 'ilus circuit extends from ground G through springs T9 and S4, winding 19, Winding contact 103 and armature 43 to battery lead S3. thence through battery B to ground The armature :2- and plunger arm 2l are attracted upon the closure. of this circuit. The attracting ot' the armature Z3 breaks the circuit of the winding 'll and alsowcon nects the line to the normal conductor Si? by the engagement ot' springs Nl and 85. llelore the armature 25 falls back upon the breaking of the circuit ot the line winding.

2l. a circuit is closed through the cut-oliI winding 2() in the following manner: The plunger arm 2l. upon being attracted. closes a circuit extending from ground tl" through the lower winding of the double-wound line relay lil of the selector li. side switch wiper (31. springs 233 and 3'2. line iti. substation circuit. as before described. line l5. springs 2h and 2T. side switch wiper G0 and upper winding ot the relay -Jffl to battery. thence through battery ll to ground (l. rl`he. relay if energizes over this circuit to shift the spring ST out of engagement with the spring and into engagement with the spring Slt.

which closes a circuit extending from ground (l4 through the springs ST and SS) and relay 5h to battery lead Sil. thence through battery B to ground (1i. The relay 5h upon energizing. shifts the spring 5N) out of engagement with the spring fil and into engagement with the spring 92 and closes contact between springs Sliand 94. The shifting ol' the spring 90. asilescribed. preparesthe circuit of the Vertical magnet to receive impulses. 'lhe engagement ot springs lll-l and ill closesl a circuit extending from ground (it through the springs 9B and fil. springs 29 and 2S and winding to battery il, thence through battery to ground. The plunger' being thus in an operated position is held by the winding 2l). ln its operated position the plunger slnrrt-circuits the auxiliary winding 12' by closing the springs 95 and 9G. This shortcircuiting ot' the winding 2:2 helps to retain the armature in an operated position for a moment. thus causing the relay to deinergize slowly. A circuit is closed to the connector private bank contact of the calling line. This is to prevent another party troni calling the substaticn A while it is calling. rThis guarding circuit extends Vt'roiu ground (il through springs il?) and ill. springs 2U .and 2S to the private normal conductor *.PT.

thence lo the banks of all olf the connectors that hare access to the line ot' substation ll'hen the springs :".o and ill are closed by the plunger. a circuitis completed through the relay fit1' of the mjaster switch D. IIbis circuit extends from ground Gr through springs 30 and 2951, contact 37, wiper 39. common segment 3S andrelay- 98, to battery lead S3, 'thence throughliattery B to. ground'. Gr... The relay 98, upon energizing, closes a.

circuit through the relay 99, `which .in turn short period of time elapses'loetween the guarding ground to the private bank contact duringy this time. 1t will be rememhere'd that the relay 51 was energized in series with the rotary magrnet and, being a slow relay, it remains held up a short time aviter the side switch has passed to Ithird position, thereby putting' a `ground on the. private wiper from `ground G through the springs 117 and 115 and wiper 62 to the private wiper 25. lt is evident that the relay 513 must be slower than 'the relay 5t in order to prevent the switch from releasing. The second selector operates for the second digit 2 in the same manner as described vtor the first selector to extend the lines to the connector H over the conductors 11S and 119. The relay G8 of the connector' l-l energizes upon the passing ot the wipers 121 and 122 ct the selector' F to third position. and closes the circuit of the relay 123,`

as in the selectors. The apparatus is now in readinessA for the third digit 2. The suhscriber operates the dial tor the third digit 2 as tor the two previous digits, The relay or# denertizes twice to close a circuit through the vertical magnet 6) extending trom ground@0 through springs 125 and 121.-sprins 127 and 12 magnet (39, side switch wiper and relay 129 to hattery lead 8?. thence through battery B to `ground (i. The vertical magnet energizes over this circuit to raise the shalt and shaft wipers (35. (3G and 67 two steps and opposite the second level of bank contacts. As soon as the shaft is lifted the springs 135% and 134.

engage. putting' battery on the release magnet 71. The relay 129 also energizes in the circuit with the vertical magnet to cause. springs 135 and 1% to engage and to cause springs 'lil-t3 and 137 to break contact. with springt- 15% and 1235. respectively. The engranient oft .grings 135 and 13G closes a, cirri t through the private magnet 72. This eirrui' attends Vfrom {Ironnd G through springs l l and 126 and private magnet 72 to hai'tcrjv lead Sii. thence through battery 1% to around t?. The relay 129 ener-grises npon t z-t impulse and. being slow-acting. does not deinerfri'fze during the momentary interruntii'in ol the circuit. but remains held up until the last impulse lias'lieen delivered. is soon as itdoes deiinergize, howeyermit breaks the circuit ot the private magnet, which in turn deenergizes to allow the. .side switch to pass to the second position. 'lt should be stated that as soon as the relav 123% energ'iaes. the engagement of d il puts a guarding ground springs x30 an on the privati bant: ot all the second sesprings 125 and 126.

lectors that have access to the connector H. rThis circuit extends troni ground G12 through theside switch wiper 77 (in first position). springs 1l() and 139 and conductor 141 to the private bank Contact 142 ot the second selector. circuit continues from this grounded contact 142 through-the private wiper 1--t2. wiper 1&3, springs lait and 145 to the point 146, and from the point 146 one branch goes through the relay 110 to hattery. and anothenhranch goes through the side switch wiper 111 over a circuit that has once been traced through the relay 5G ot the first selector. These relays 56' and 110 are thus heldin an energized position.

Returning again to that point where the side switch ot' the connector is allowed to pass to the second position, the passing of the side switch wiper 76 to the second position disconnects the vertical magnet from and places the rotary magnet in the circuit with the slow relay 129. -The apparatus is now in position to receive the impulses 'for the fourth or last digit 0. As the dial is operated for this digit the circuit ot' the relay (58 is broken ten times,- as before. The relay G8 denergizes ten times, each time closing a circuit extending from ground G1 in. thereby permitting the side switch to pass to the third position. The passing of the wipers 73 and 74: to the third position connects the calling line to the called substation through the condensers 149 and 150. The passing of the wiper 77 to the third position shittsthe'holding ground for the release relays 110 and 56 ot' the selectors from ground (il2 to ground G10 through the In its third position the wiper 75 serves to place ground on the relay 58. and also completes the circuit of the winding 153 of the line switch C. This lastv circuit extends from ground G13 through the side switch Wiper 75, springs 151 'and 152 to the private wiper 66, conductor 15st and windingr 153 of the line switch to the battery lead S3, thence through battery B to ground G. The armature is attracted, thereby disconnecting the liney winding 160 vfrom the called line, and also extends the conductor 161 to the line 158 hy closing the springs 156 and 157. The side switch wiper 76 ot' the connector, in the third. posit-ion, serves to close the circuit of the ringer relay 57. This circuit extends trom ground G1 through the interrupter 78,

los

springs 1112 and 163, ringer relay 57, side rite i ii'iper 'ill and relay 129 to the battery lad S33, tlienoe through batterytogroiind. The ringer relay is energized interniittently i 'o disconnect the calling line and connect the trailed line with lthe ringing euri-ent generator li, .iriinging current then extends from generator L through springs 164 and 165, le sri'itrli Wiper 74:. shaft iviper 65, springs 155i and ifi?, line conductor 158, bell 170, iairuleiiser 171 (assuming that there is but oi :iet oi" hells on the line), line 159, wiper "1li", .side switch wiper 73 and springs 168 yand 117 to the other side of the generator L. 'i` .e siiliserihei at substation A removes the iii'eixiii response to the signal, and therehy closes an energizing cireiiit as soon as relay 5T again deiinergiiies, should it he puiled up at 'the time, through the haekliridge relay of the connector. This cireuit entends frein ground Gd through side Y 'wiper Tfn-lower winding of relay 58, i' i 1131? and 11312, side switch wiper '73, shaft wiper GT, line 151i, springs 172 and 173, pulse springs, receiver 174. trimsinittei il'l'l'" l 'il si'irings 1Go and 1Go, and upper oi? relay 5d. to liattery lead S3, n. through battery B to ground. Thus ralled suliscrilier is supplied with talking hattii'y euri-ent. The relay 5S energizes over the circuit just traced to break the eircuit ol the. ringer relay 57 at springs 162 and 11.33.

lifter 'the eoiii'ersatiion is completed, the release et the central o'llce apparatus used in the foregoing ral! is initiated hy .the calling l i" 'rilier hangin?" u.) his reeeiver. The releise is as 'liolloii'm rllie breaking of `the iarureut ot springs l and 7 at the calling siihiwautioii breaks the cireiiit through the relai# litl olr the ronnertoi'` which in turn deei'iergiiies. tlijereliy lirealing the holding ground i'or release relays 123. 11() and 5G oi' 45 the roiuiertor ll land selectors F and E, re-

spi tively. rThese relays each deiinergize aud close the ririfui't-s oi thev release iiiagnets ot' their respective switches. The cirruit or' the roiineetor release magnet 71 extends `from il ground (im through springs 125 and 121, springs-i 127 and li'l, magnet 71 and springs 135i and 'lillto battery. '.l`lie energircation of the release magnet permits the su'iteh to return to norinal pori- 5.5 lion, therein separating the springs 133 and lslf. The (tiri-uit oi" magnet 17T ol.E selector ll` extends lroiii ground (iw, through springs 1TH and 17S), springs 15%() and 181, magnet li'i'. springs' 18;) and 1h11 to liattery lead S3, llieiire through battery P to lground (i. The seleetor lf) releases over a rireuit similar to that ol seieeiior l". The Contact between sprii :'12 and Vffl. 1512? and 1925 of" the selecf tors in and l?, resilaa'tii'ely, hroken as the sliats return to their normal positions. The

rie S. springs 15T and 151i, nipeis (i5- denergizing of relay 56 also breaks the holding circuitl of the win din of the ling switch C. Thus all of the sllvitches are restored to normal position and are in readiness for another call, i

Returning now to that poinf'in the operation of the connector While the side switch is yet in the secondv postion, had' the called line been busy, the Aside switch would not have passed toithe third position, but would 'have been looked in the second position by the private magnet remaining energized.4

The circuit through the private magnet would have been from the bank Contact upon' which the Wiper 66 is resting, which contact would have' geen grounded, through the wiper (36, springs 152 und 151, lower Winding of the relay 58, ringer springs 169 and 168, wiper 73 (in second position), springs '13S and 136 and private magnet 72 to butground G1, and also give" the calling sub-- seriher the busy signal over a circ-uit extending vfrom the battery lead S3 through the secondary of induction coil 188 of the busy signaling' machine M, springs 18S) and 190, side switch Wi per TA1 (in second position), springs 165 and 1Go. condenser 11119, thence orer the heavy Conductors to and through the suhstaiition A, haelt over the heavy condiietors through the lower `winding of the relay (5S to`fguuind. thence to the starting point.

Tlieohject in haring the ground shifted1 ironi the private wiper (56 to ground (im is to prevent the side sriiteh from deni'argizing shouldt'lie guarding potential he removed before the switch 'li-l has heen released. The release of the switches in oase the ealled lineis liiisy is the saine as it' the connection had heen obtained.

It haring heen explained lioiiI a eoiineov i tion is extended `troni one line to another,

it will now he 0X )laiiied how the subscribers at two siihstatlorns op the saine line, substations A and A,,'tor instancel mayf eonrei-se without manipulating the central oi'iee ai'iparatus. lf a part,7 atsuhstation A desires tooiiverse with! a iiart-y at substation rv, all that is necessary for him .to do is to remove his receiver after haring signaled the other part)7 liy means ol the buzzer Cir-f ruit lx'. Sullicient vtalking battery eiii'rent is supplied to the Aparties for theni to non reise. hut enough current does not flow `to pull up the armature 25, due to the resistance 18. The two substations are provided with talking battery current from the central ollice over a circuit as follows: From ground G,'spri.ngs 79 and 80, resistance 18, line 16, through both substations in parallel, as before described, haelt over the line springs 81 and 82, line winding 21 to the battery lead 83, thence through battery B to ground G, Although suiiicient current flows over this circuit to energize the transmitters at the substations, 'the resistance 18 prevents the current from being strong enough to cause the armature E25 to be attracted by the winding 21, as previously explained. Thus it is evident that yno switches at the central oflice are made busy during the time that any of the parties on the same line are conversing.

Should lthe subscriber at substation A desire to converse with the subscriber at substation A2, he calls the station A3. The pai y at substation A3`then signals the subscriber A2, assuming that there is but the one set of bells 170 bridged across the line.

Thus it will be seen that provide an extension or party-line system in which provision ismade for preventing actuation of the line switch when the line is used for intercommunieating purposes, and in which the said switch is controlled over the two sides of the line in series, current for talle ing purposes being derived from a common battery or other central source, Se far as I am now aware, therefore, it is new to enable two common. battery subscribers on the same line to be supplied with talking current from a central source'without operating any switches of the system.

that l claim as my invention is :J-

L In a telephone system, a telephone line,

av plurality of telephones for said line each `provided with means for intercommunicatt ing over said line, automatic trunlnng apparatus 1n which? the line terminates, means operative to supply current over the line from the central station to two of said tele` phones when the said line is used for intercommunicating purposes, and means for preventing the normal condition of said trunking apparatus being disturbed under such conditions.

2. ln a telephone system, a subscribers line, a plurality of telephones for said line. each provided with means for intercommunicating o ver said line, an automatic trunking switch for said line, means operative to supply current over the line from the central station to two of said telephones when the said line is used for intercommunh ating purposes. and means for preventing' the normal condition ot said trunking apparatus being disturbed under such conditions.

In a telephone system, a subscrilwr`s line,.trunl line, means for automatically se- .selecting idle trunks a plurality lecting idle trunks ahead of the calls, switching apphratus for connecting the subscribei"s line with a preselected trunk line, a plurality of telephones for said subscribers line, means for supplying talking current 'owl' the subscribers line to said telephones. and means preventing actuation of said siwitching apparatus when a person at one. telephone uses said current for conversi with a person at another telephone on the same line.

el. ln a telephone system, a subscrihers line, a plurality ot telephones for said subscribers line. an automatic switch line, means for supplying talking current through said switch to the line. a resistance -for preventing actuation otl said switch when aperson at one telephone converses with a. person at another telephone on the same line, and means at each telephone for shortcir! cuiting said resistance to cause the actuation of said switch when connection with another line is desired.

In a telephone system. a telephone line,

va plurality of telephones for said line. automeans operative to supplycurrent over the line Jfrom the central station to two of said telephones when the said 'line is used for intercommunicating purposes, means tor prei'enting the normal condition of vsaid trunking apparatus son at one of said telephones may signal a person at another telephone on the saine line.

7. In a telephone system, a subscribers line. trunk lines. means Jfor automatically ahead of the calls, switching apparatus for connecting the subscriber`s line with a preselected trunk line,

of telephones 'for said sub'- scribers line. means tor supplying talking currentv over the subscrihe1"s line to said telephones. means preventing actuation oi? said switching apparatus when a person at one telephone convex-ses with a person at another telephone on the same line. and means whereby a person at one of said telephones may signal a person at another telephone on the same line.

S. ln a telephone system. a subscribei"s line, a plurality of telephones for said subv being disturbed under such conditions, and means whereby a perior said l rality of telephone talking with Said line, im zultonmtcally progressiviy movable switch foi: said line, another lim?u means for operating the Suid switch to Extend a connection from the filas?, to the svcmid, ine, :l buttery for suppyiug current to the circuits of said system ifm' operating piiiwses, means Vfor Supplying; current tn tl1e-i'i11e-th10ugh said switch lfor energizing (minted the snid'tnlking sets, :1nd for prevdutilig the 10 operutwii of Suid swltch as n result.

Signed. bv me at Chicago, Gool; county, llinols, thm 2T day of April, 19ML TALB( )T G. MA RTI N.

Witnesses EDWARD D. FALES, ARTHUR J. RAY. 

